Fuel injectors are well known per se and typically supply fuel under pressure from a fuel pump directly to a needle valve within the injector housing. A coil surrounds an armature coupled to the needle valve. Upon energization of the coil, the needle valve is moved to a valve-open position to supply fuel under pressure to the internal combustion engine. Upon deenergization of the coil, the needle valve returns to its closed position under the bias of a spring.
In high pressure fuel systems, an external pump is conventionally used to pressurize the fuel. The pump is typically driven by an electrical motor or solenoid. In certain systems, the fuel is pressurized by a system driven mechanically off of the drive shaft. These systems, however, have proven complex and energy-inefficient.
Further, injectors are also known in which combustion chamber pressure is employed to pressurize the fuel at least to the pressure of the combustion chamber. For example, in U.S. Pat. No. 4,197,996, there is illustrated a fuel injector having a spring-biased piston having one face exposed to the pressure in the combustion chamber and the opposite face exposed to a fuel chamber within the fuel injector. During the compression stroke in the combustion cylinder, the piston within the fuel injector is displaced to pressurize the fuel to a pressure corresponding to the combustion chamber pressure level plus the force of a spring. When the coil is energized, the armature is displaced to open the valve, injecting fuel into the combustion chamber at a pressure level equal to the force of the spring. This arrangement provides a constant charge pressure to the fuel injected into the engine unaffected by changes in combustion chamber pressure levels.